A bandgap voltage reference circuit is a temperature independent voltage reference circuit widely used in integrated circuits. Such a circuit is designed to produce a fixed voltage regardless of temperature changes. One example of a bandgap voltage reference circuit combines a complementary to absolute temperature (CTAT) circuit and a proportional to absolute temperature (PTAT) circuit to obtain a voltage relatively insensitive to temperature. One example of such a circuit is a Brokaw bandgap reference circuit.
The temperature coefficient (temp-co) of both CTAT and PTAT voltages should to be equal to obtain a zero temp-co of the reference voltage. Generally, the PTAT voltage has a lower temp-co and should be multiplied to obtain the temp-co in order to cancel the temp-co of the CTAT voltage. In a reference circuit, it is generally the PTAT voltage circuit that generates the most noise. Multiplying the generated PTAT voltage to obtain the temp-co also multiplies the noise.